<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div style="background-color: pink;">
    <div style="height: 100px;border: 1px solid yellow;">
        header
        <ul style="list-style-type: none;">
            <!-- <li>1</li>
            <li>2</li>
            <li>3</li>
            <li>4</li>
            <li>5</li> -->
        </ul>
    </div>
    <div style="height: 300px;">
        <div style="float: left;height: 100%;width: 20%;border: 1px solid yellow;">
            aside
        </div>
        <div style="float: left;height: 100%;width: 79%;">
            section
        </div>
    </div>
    <div style="height: 100px;border: 1px solid yellow;">
        footer
    </div>
    <div style="font-size: large; position: fixed;top:1px;right:1px;width: 10%;height: 10%;background-color: aqua;display: right ;" id="mask">
    test
    </div>
    </div>
</body>
</html>